Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Stratified or layered articles
Reexamination Certificate
2003-05-21
2004-03-16
Ruddock, Ula C. (Department: 1771)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Stratified or layered articles
C264S125000, C264S128000, C264S176100, C264S239000, C264S257000, C427S202000, C427S206000
Reexamination Certificate
active
06706225
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a laminate composite material having a water vapor transmission rate (WVTR) exceeding one (1) perm of water vapor where perm (permeance) is in grains/hr. ft.
2
in.Hg. More particularly, the invention is directed to a laminate composite material which substantially blocks the flow of air and water, but which allows the transmission therethrough of water vapor or moisture vapor. The composite material includes a layer of open weave supporting fabric and a film of a breathable resin wherein the layer and the film are adhered to one another by a high temperature volatile particulate added to a thermoplastic resin wherein the resultant composite material has a water vapor transmission rate exceeding one (1) perm of water vapor.
BACKGROUND OF THE INVENTION
It is known that breathable building wraps, also referred to as housewraps, are used and provide advantages in the construction of wall and roof assemblies. These housewrap materials improve energy loss through reduction of air infiltration as well as acting as a weather barrier by preventing water intrusion into the building. It is a requirement that these materials are breathable, as defined by a minimum level of water vapor transmission rate (WVTR). Two popular materials that are manufactured for housewrap that achieve the combination of a barrier to water intrusion and air infiltration while remaining permeable to moisture vapor are a flash spunbonded polyolefin that may be obtained from DuPont under the name Tyvek™. A second material is a microporous polyolefin film composite and may be obtained from Simplex Products under the trademark “R-Wrap™.”
BACKGROUND OF THE PRIOR ART
It is known to use porous polyolefin films composites in housewrap applications. Housewrap materials must be permeable to gases as to allow water vapor to escape from the wall to which the film is secured. Otherwise, condensation of the water vapor trapped inside the wall may occur which leads to rotting and the growth of fungus, mold and mildew which may damage the wall. The film must be sufficiently impervious to air to insulate the wall against wind and water intrusion. Further, the film must have adequate tensile and physical properties such as break strength, elongation, tear strength, shrinkage and puncture strength to avoid damage during installation.
It is also known to prepare porous polyolefin films by stretching a precursor film filled with calcium carbonate. “Breathable” films which are gas/vapor permeable and liquid impermeable have been described in U.S. Pat. No. 4,472,328, assigned to Mitsubishi Chemical Industries, Ltd. The Mitsubishi patent describes a breathable polyolefin film prepared from a polyolefin/filler composition having from 20 percent to 80 percent by weight of a filler such as a surface treated calcium carbonate. A liquid or waxy hydrocarbon polymer elastomer such as a hydroxy-terminated liquid polybutadiene was found to produce a precursor film that could be monoaxially or biaxially stretched to make a film breathable. The breathable film described by Mitsubishi is also described in Great Britain Patent No. 2,115,702, assigned to Kao Corporation. The Kao patent further describes a disposable diaper prepared with a breathable film as disclosed by the Mitsubishi patent. The breathable film is used as a backing for the diaper to contain liquid.
It is also known to laminate porous polyolefin films, also referred to as microporous films, to open mesh fabrics as described in U.S. Pat. No. 4,929,303 assigned to Exxon Chemical. In the Exxon patent an open mesh fabric known under the trade designation CLAF, as manufactured by Amoco Fabrics, and a microporous film known under the trade designation Exxaire™, as manufactured by Exxon Chemical, are laminated together, without the addition of an adhesive. Wherein the fabric is heated on a hot roller and then pressed into contact with the unheated film creating a bond between the two layers. This technique is known in the art as “thermo bonding.”
It is also known to bond or adhere two or more layers one to another with the use of various mastics or adhesive coatings. But use of most known adhesives, mastics and coatings when applied between a fabric layer and a microporous film seal the micropores of the film rendering it non permeable to water vapor and thus it becomes non functional and totally ineffective.
Further, as described in the Exxon patent an open mesh fabric is required in the composite to add strength and maintain permeability to water vapor and allow free passage of water vapor through the microporous film and continue generally unimpeded through the openings in the fabric.
It is known in the industry that when adhesive coatings are applied to open mesh fabrics it is possible for the adhesive to migrate through the openings in the fabric. This uncontrolled migration of adhesive, bonds each internal “top” layer to the succeeding “bottom” layer as the completed composite is rolled up on a take up reel. Hence, each concentric layer is bonded to the next on the accumulated roll and cannot later be unrolled. This is a highly undesirable condition unrolled condition known in the art as “blocking.”
It is known to add high temperature volatile materials, sometimes referred to foaming agents to thermoplastics for the purpose of creating closed gas cells resulting in the lowering of the density of the finished material. This is a common practice in the injection molding process but not common in the extrusion film process.
SUMMARY OF THE INVENTION
There has surprisingly been discovered an adhesive material and process for applying same that would bond microporous films to open mesh fabrics that would avoid sealing of the micropores and thus maintain the high permeance (WVTR). Said adhesive material also avoid “block” of the internal layers within the rolled up composite.
Also contemplated is a process for preparing the laminated composite. The process comprises steps of specially preparing a polyolefin resin extruding that resin through a die to form an adhesive layer between a microporous film and an open mesh fabric. The resulting composite would be substantially impervious to water and air yet having a high water vapor transmission rate (WVTR) and would exceed a minimum of 1 perm of water vapor. The invention utilizes conventional equipment that is well known in the art.
The laminate composite according to the present invention is especially well suited as a building wrap or roof underlayment but could be useful in other industrial and consumer applications.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The laminate construction material according to the present invention comprises a layer of an open weave supporting fabric adhered to a microporous or a monolithic film by a layer of dry adhesive slit film that is heated and then introduced between said layers thus acting as a bonding agent. The film layer may be microporous or monolithic, being substantially impervious to water and air and having a water vapor transmission rate greater than 1 perm. A microporous film is manufactured by conventional methods of extrusion or casting a polyolefin resin with added fillers followed by monoaxially or biaxially stretching as to form interconnected voids. A preferred microporous film is designated under the name Exxaire™ and obtained from Exxon Chemical (now Tredegar).
The composite material of the present invention may be prepared by utilizing conventional extrusion and laminating equipment. The prepared resin with a high temperature volatile particulate additive is melted in a conventional extruder and extruded through a die to form a layer of molten resin which is deposited onto the web of open weave supporting fabric. Simultaneously a web of microporous film is introduced on the opposite side facing the open mesh fabric. The entire assemblage is passed through the nip of two rolls. One nip roll has a controlled temperature that chills the molten resin and causes it to solidify, while the other nip roll is used to control ni
Fraser Donald R.
MacMillan Sobanski & Todd
Ruddock Ula C.
Tyco Plastic Services AG
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